5. The analyzer of claim 1, wherein the detector comprises an ion chamber
filled with a gas selected from He-3 and BF.sub.3.

6. The analyzer of claim 1, wherein the shielding source holder comprises
a first end, a second end opposite the first end, and a substantially
circumferential side wall.

7. The analyzer of claim 6, wherein the shielding source holder comprises
a handle receiver formed in the first end and a neutron source receiver
formed in the second end, opposite from the handle receiver, wherein the
neutron source receiver is configured to receive the neutron source, and
wherein the handle receiver is configured to receive a source handle
assembly.

8. The analyzer of claim 7, further comprising a press fit cover disposed
within the neutron source receiver.

9. The analyzer of claim 1, wherein the neutron source is encapsulated in
a stainless steel capsule.

10. The analyzer of claim 9, wherein the neutron source assembly further
comprises a spring washer disposed between a top side of the capsule and
the shielding source holder.

11. The analyzer of claim 9, wherein a circlip is disposed at a bottom
side of the capsule.

12. The analyzer of claim 1, wherein the shielding source holder
partially surrounds the neutron source, such that the shielding source
holder is between the neutron source and the detector.

13. A method for measuring neutron signals, the method comprising:
detecting background in a detector system; placing a target within the
detector system; measuring a total signal for the detector system; and
determining the neutron signal for the detector system.

14. The method of claim 13, wherein determining the neutron signal
comprises subtracting the background detected by the detector system from
the total signal measured by the detector system.

15. The method of claim 13, wherein the detector system comprises: a
detector; and a neutron source assembly adjacent to the detector, the
neutron source assembly comprising: a neutron source; and a shielding
source holder.

16. The method of claim 15, wherein the shielding source holder comprises
a material selected from lead and tungsten.

17. The method of claim 15, wherein the detector comprises an ion chamber
filled with a gas selected from He-3 and BF.sub.3.

19. The method of claim 13, wherein detecting background in the detector
system comprises disposing a blank target in the detector system.

20. The method of claim 19, further comprising removing the blank target.

21. The method of claim 15, further comprising measuring neutron signals
for the detector system without the shielding source holder, comprising:
detecting background in the detector system, wherein the shielding source
holder is removed; placing a target within the detector system; measuring
total signal for the detector system having the target therein; and
determining the neutron signal for the detector system, wherein
determining comprises subtracting the background detected by the detector
system from the total signal measured by the detector system.

Description:

FIELD OF INVENTION

[0001] Embodiments disclosed herein relate generally to high-energy
radiation detection. In particular, embodiments disclosed herein relate
to separation of neutron signal from gamma signal. Specifically, it is
found that certain materials used to stop gamma rays also can increase
the neutron flux to the detector.

BACKGROUND

[0002] Neutron flux is typically measured by the effect of interactions
between neutrons and their surroundings. For example, neutrons may
interact with a material to be detected, and thus create a measurable
effect. Detectors may be used to detect such effects, which may include
high-energy and ionizing radiations resulting from absorptive reactions,
activation processes, and elastic scattering reactions, for example.
"High-energy radiation," as used herein, refers to radiation of neutrons,
X-rays, gamma rays, α particles, and β particles.

[0003] Detectors of high-energy radiation may include, for example, ion
chambers, proportional counters, Geiger-Mueller counters, and
scintillation counters. FIG. 1 shows an exemplary prior art detector that
may be used to measure hydrogen content by detecting thermal neutrons
reflected back from a target. As shown, a basic system 10 for neutron
detection includes a target chamber 13, an ion chamber 14, and
electronics (not independently illustrated). Fast neutrons 12 are
produced by a neutron source 11. These fast neutrons 12 interact with
hydrogen nuclei H in the target chamber 13 until their velocity is
reduced to the average thermal velocity of the target through a process
known as neutron moderation. Specifically, neutron moderation involves a
collision and energy transfer from a fast neutron to a target nucleus,
wherein the velocity of the fast neutron decreases to that of a slow
neutron after the collision and energy transfer. The thermal (slow)
neutrons are then scattered from the target chamber 13 to the ion chamber
14.

[0004] In the example of a commonly used neutron detector shown in FIG. 1,
the ion camber 14 may be filled with a gas (such as He-3) that may
interact with the thermalized neutrons to produce ions. When a He-3 atom
absorbs (captures) a thermalized neutron, a nuclear reaction occurs and
the resultant products are a positively ionized tritium (H-3) atom and a
proton. The positively ionized H-3 atoms and protons travel through the
gas, pulling electrons in their wake and thus creating an equal number of
positive ions and electrons. When a potential is applied across the
electrodes 40, 45 in the ion chamber 14, the positive ions are swept to
the negatively charged electrode and the electrons are swept to the
positively charged electrode, producing currents that are directly
proportional to the number of ions transferred. The number of ions
transferred depends on the rates of their formation and hence the neutron
flux. Thus, the ion currents measured by the ion chamber may be used to
derive the magnitudes of the neutron flux, which may be used to determine
the amount of hydrogen in the target material.

[0005] However, the ion currents generated in these processes are
extremely small (on the order of 10-12 amp), making it difficult to
accurately determine neutron flux. In addition, temperature and humidity
changes in various electronic components, cables, etc. may further
compromise the accuracy of the measurements. The situation is even worse
under field conditions, which often include wide variations in
temperature and humidity.

[0006] While prior art high-energy radiation detectors are capable of
providing satisfactory measurements, there remains a need for detectors
that may provide more reliable and accurate measurements of high-energy
radiations.

SUMMARY OF INVENTION

[0007] In one aspect, embodiments disclosed herein relate to an analyzer
having a detector and a neutron source assembly adjacent to the detector,
wherein the neutron source assembly has a neutron source and a shielding
source holder.

[0008] In another aspect, embodiments disclosed herein relate to a method
for measuring neutron signals that includes detecting background in a
detector system, placing a target comprising a moderating material within
the detector system, measuring a total signal for the detector system,
and determining the neutron signal for the detector system.

[0009] Other aspects and advantages of the invention will be apparent from
the following description and the appended claims.

[0012]FIG. 3 shows a cross-sectional view of a moisture analyzer
according to embodiments of the present disclosure.

[0013]FIG. 4 shows a cross-sectional view of another embodiment of a
moisture analyzer in accordance with the present disclosure.

[0014] FIGS. 5A and 5B show a cross-sectional view and a perspective view,
respectively, of a neutron source assembly according to embodiments of
the present disclosure.

[0015]FIG. 6 is a graph of the amount of signal and background detected
in moisture analyzers according to embodiments of the present disclosure.

[0016]FIG. 7 is a graph of the amount of neutron signal detected in
detector systems according to embodiments of the present disclosure.

DETAILED DESCRIPTION

[0017] Embodiments of the invention relate generally to detector systems
for measuring high-energy radiation, and in particular for increasing and
measuring neutron flux. Neutron flux, as used herein, refers to the
amount of neutrons passing through an area over a period of time.
Detector systems used for measuring neutron flux may rely on neutron
moderation, i.e., a process of bringing fast neutrons into thermal
equilibrium. In particular, as neutrons are generated from a neutron
source, the neutrons are released having high kinetic energy, which are
referred to herein as "fast neutrons." In accordance with energy
conservation laws, the high kinetic energy of fast neutrons may be
reduced (moderated) by colliding with and transferring energy to
moderator material. Upon transferring energy to a moderator material, the
speed at which fast neutrons travel reduces, thus giving the
post-collision neutrons the name slow neutrons. Due to the relationship
between neutron kinetic energy and neutron temperature, slow neutrons may
also be referred to as thermal neutrons after fast neutron moderation.

[0018] Further, using moderator material having a low atomic number may
allow for more efficient energy transfer. For example, the collision of a
fast neutron with a hydrogen nucleus, which has substantially similar
atomic mass as a neutron, may result in substantial reduction of energy
in the fast neutron, thereby generating slow detectable neutrons at a
faster rate. Accordingly, detector systems may use hydrogen-containing
moderator materials (like water) for neutron moderation and detection.
Additional examples of moderator material include graphite, polyethylene,
polypropylene, polystyrene, and other plastics, alcohol, oil, and other
organic material, coke, iron pellets, hydrocarbon material, and other
materials having a low atomic number, high scattering cross section, and
low absorption cross section. As used herein, hydrogen-containing
materials refer to a type of moderator material. However, regardless of
the target material, embodiments disclosed herein allow for increased
measurements of neutron flux while also providing gamma shielding.

[0019] Such detection processes may likewise be used for moisture
analysis. For example, embodiments of the present disclosure may utilize
mathematical correlations between the amount of slow neutrons detected
(i.e., neutron flux) from neutron moderation with a hydrogen-containing
material such as water to provide information regarding the amount of
hydrogen nuclei present, and thus provide means for analysis regarding
the amount of moisture present.

[0020] FIG. 2 shows a conventional moisture analyzer 10 having a toroidal
(donut) shape detector 14 with a neutron source 11 disposed within the
detector 14. As shown, neutron source 11 generates fast neutrons 12 and
gamma rays γ. For example, along with emitting fast neutrons, a
commonly used neutron source, americium-beryllium (AmBe), may emit about
4.43 MeV γ. Other neutron sources may include americium-lithium
(AmLi), radium-beryllium (RaBe), or plutonium-beryllium (PuBe), for
example. Other industrial neutron sources include a neutron generator
which is a direct action electrostatic accelerator (ion gun). In a
neutron generator, deutrons accelerated to about 80 keV may hit a
deuteron or tritium target, the collision of which may produce neutrons.
These sources may be more powerful than the isotopic sources but more
expensive and with a shorter life than Am/Be. Thus, a neutron generator
may commonly be used where the desired high neutron flux cannot be
achieved with isotopic sources. Additionally, a neutron generator may be
capable of operating in a pulse mode.

[0021] A fraction of the fast neutrons 12 emitted from neutron source 11
will scatter into the target chamber 13, which may be filled with
hydrogen-containing materials (like water). The fast neutrons 12 collide
with the hydrogen nuclei in the target chamber 13. Hydrogen nuclei, with
a similar mass as that of a neutron, are very efficient in slowing down
the fast neutrons and eventually bringing them into thermal equilibrium
with the environment (neutron moderation). As a result of the
interactions with hydrogen nuclei, fast neutrons lose kinetic energy and
become slower (thermal) neutrons. For example, upon interactions with
hydrogen nuclei, thermal neutrons may have an average energy equal to the
energy of thermal motion (25 meV) at room temperature. Thermal neutrons
may then undergo diffusion similar to gas diffusion, and some of the
thermal neutrons may return to the detector 14 to be measured as neutron
flux.

[0022] Detector 14 is an ion chamber filled with a gas having nuclei that
can capture thermal neutrons and undergo nuclear reactions after neutron
capturing. Such nuclei include: boron (B-10, e.g., BF3), lithium
(Li-6), helium (He-3), uranium-233, uranium-235, and plutonium-239. Among
these, He-3 gas has the advantage of having a large thermal neutron cross
section (5330 barns) and, therefore, is commonly used in the ion chamber.
Although B-10 (used in BF3 reactions with neutrons) has a lower
thermal neutron cross section (3840 barns) than He-3, BF3 may also
commonly be used in the ion chamber due to its availability. However, one
of ordinary skill in the art would appreciate that embodiments of the
invention are not so limited. In fact, embodiments of the invention may
use any gas or other medium capable of ion transport that can produce
ions by the high-energy radiation of interest.

[0023] Detector 14 is sensitive mostly to thermal neutrons and much less
so to fast neutrons 12 and gamma rays γ. However, detected thermal
neutron flux may be lower since only a few neutrons come back to the
detector due to diffusion. The result of relatively high gamma detection
is referred to as gamma background, which may contribute to total
background noise, i.e., detector signals not related to the presence of
hydrogen. Background noise is typically higher in BF3-filled
detectors than in a He-3-filled detectors.

[0024] Neutron flux may be measured in an ion chamber detector by applying
an electric potential across a pair of electrodes in the ion chamber. For
example, in an He-3-filled detector, two electrodes may be positioned
parallel within the detector to measure current flowing in the He-3 gas
as a potential is applied between the electrodes. He-3 gas typically
serves as an insulator, and, therefore, no current (except for a small
leakage current) is detectable between the two electrodes. However, when
an He-3 atom absorbs (captures) a thermal neutron, a nuclear reaction
occurs as follows:

23He+01n→13H+11p (1)

This nuclear reaction produces a tritium (H-3) atom and a proton. He-3
and H-3 are isotopes of helium and hydrogen, respectively. This reaction
also releases an energy of approximately 764 keV (i.e., Q-value=764 keV),
and, therefore, the tritium and the proton are produced with high kinetic
energy. The tritium and proton travel at high speeds through the gas,
pulling electrons in their wake to create an equal number of positive
ions and electrons. The positive ions and electrons serve as charge
carriers in the gas, which is otherwise an insulator.

[0025] If a voltage is applied across a pair of electrodes within an ion
chamber detector, an electric field is created in the space between the
electrodes. The ions move in response to this electric field with the
positive ions and electrons pulled in opposite directions toward opposite
electrodes. The ions are eventually neutralized at the electrodes,
resulting in an ion current that is directly proportional to the number
of positive ions transferred to the electrodes. Such an ion current may
be measured. Further, the number of positive ions transferred to the
electrodes is in turn proportional to the thermal neutron flux.
Therefore, the ion current measured from the electrodes may be used to
derive the magnitude of the thermal neutron flux through ion chamber.

[0026] The positive ions and electrons present in the ion chamber may also
collide and then recombine to form a neutral atom. This recombination
competes with ion and electron transport to the electrodes, and, thus,
reduces the measurable magnitudes of the ion currents. In the absence of
an applied voltage across the ion chamber, there will be no ion transport
and the positive ions and electrons will eventually recombine. When
voltage is applied across the electrodes, the positive ions are pulled
toward the negatively charged electrode and the electrons are pulled
toward the positively charged electrode, reducing the probability of
recombination. If the voltage applied across the electrodes is too small,
the positive ions and electrons travel slowly to the electrodes,
resulting in more recombination. When the voltage is high enough to pull
the electron and ion clouds apart and make recombination insignificant, a
"plateau" (also referred as "ion plateau" or "first plateau") begins to
form. The plateau ends when the voltage is high enough to accelerate the
electrons to the energy high enough to ionize gas atoms upon collision
(secondary ionization). This process is known as "proportional regime,"
and may be used in proportional counters. However, ion chamber detectors
generally do not exhibit proportional regime, and work on plateau with
the current independent of voltage since primary ionization may be
collected without recombination.

[0027] Advantageously, the inventors of the present disclosure have found
that by using a shielding material, in particular a shielding source
holder, between a neutron source and a detector, the detector may be
shielded from gamma rays (thus decreasing gamma background) and neutron
flux may be enhanced. For example, along with suppressing the gamma
background, shielding source holders made of lead (Pb) and tungsten (W)
may also increase the neutron-related signal (neutron flux) up to 20% and
40%, respectively.

[0028] It is theorized by the present inventors that the increase in
neutron signal may be related to the neutron scattering properties of the
shielding material of a source holder. Referring to tungsten as an
exemplary shielding material of a source holder in a neutron detector,
tungsten may act both as a shield against gamma radiation and as a method
of scattering fast neutrons that would otherwise miss hitting the target
material.

[0029] In particular, FIG. 3 shows a cross sectional view of a moisture
analyzer 10 according to embodiments of the present disclosure having a
toroidal (donut) shape detector 14, such that there is a hole at the
center of the detector 14. A neutron source 11 is partially surrounded by
a shielding source holder 15 and positioned in the center of the detector
14. The shielding source holder 15 is made of a shielding material, such
as tungsten. As shown, the source holder 15 surrounds all sides of the
neutron source 11 except for a side facing the target 13, such that the
shielding source holder 15 is between the neutron source 11 and the
detector 14.

[0030] The neutron source 11 emits fast neutrons 12a, 12b. In particular,
fast neutrons 12a are emitted from neutron source 11 in a direction
directly toward the target 13. Fast neutrons 12b are initially emitted
from neutron source 11 in a direction away from the target 13 and into
the shielding material of the shielding source holder 15. Depending on
the neutron scattering properties of the shielding material of the
shielding source holder 15, the likelihood of fast neutrons 12b being
redirected toward the target 13 may increase. Although shielding source
holder 15 does not affect the fast neutrons 12a initially directed toward
target 13, shielding source holder 15 enables another mechanism of
neutron scattering, which may increase the amount of fast neutrons 12b
that hit target 13, and thus increase the total amount of fast neutrons
12a, 12b capable of neutron moderation.

[0031]FIG. 4 shows a cross-sectional view of another embodiment of a
moisture analyzer in accordance with the present disclosure. The moisture
analyzer 10 of FIG. 4 has an ion chamber detector 14 and a neutron source
11 adjacent to the detector 14. The neutron source 11 has a shielding
source holder 15 surrounding the neutron source 11, which may together be
referred to as a neutron source assembly 20. The neutron source assembly
20 is inserted in the center of the detector 14 (thus positioning the
neutron source 11 in the center of the detector 14) and held in place
with a source handle assembly 16. The ion chamber detector 14 is covered
with an ion chamber cover 17, which also acts to support the source
handle assembly 16. Moisture analyzer 10 is directed to a target 13, such
that the neutron source 11 is closest to the target 13. As shown, target
13 may include one or more materials, 13a and 13b.

[0032] Close perspective and cross-sectional views of components of an
exemplary neutron source assembly 20 are shown in FIGS. 5A and 5B. In
particular, FIG. 5A shows a cross-sectional view and FIG. 5B shows a
perspective view of a neutron source assembly 20 having a neutron source
11 surrounded by a shielding source holder 15. Shielding source holder 15
is made of gamma shielding material such as tungsten. In the embodiment
shown, shielding source holder 15 is cylindrical in shape, having a first
end 26, a second end 27 opposite from the first end 26, and a
substantially circumferential side wall 28. A handle receiver 25 is
formed in the first end 26 and a neutron source receiver 24 is formed in
the second end 27, opposite from the handle receiver 25. The neutron
source receiver 24 is configured to receive the neutron source 11, and
the handle receiver 25 is configured to receive a source handle assembly
(shown in FIG. 4).

[0033] Other sizes and shapes of shielding source holders may be used to
shield a neutron source from a detector. For example, a shielding source
holder may be shaped as a toroid, a rectangular frame, or any other shape
that may at least partially surround the neutron source. Further, a
shielding source holder 15 may have a uniform thickness or a non-uniform
thickness. For example, as shown in FIGS. 5A and 5B, shielding source
holder 15 has a non-uniform thickness t, wherein thickness t is measured
from the neutron source receiver 24 to the outer surface of the shielding
source holder 15. In particular, the first end 26 of the shielding source
holder 15 has a larger thickness than the side wall 28 thickness.
Alternatively, other embodiments of a shielding source holder 15 may have
a substantially uniform thickness.

[0034] Referring again to FIGS. 5A and 5B, neutron source 11 is
encapsulated in a stainless steel capsule 29 having a top side 29a, a
substantially circumferential side 29b, and a bottom side 29c opposite
from the top side 29a. In other embodiments, the capsule may be made of
materials other than stainless steel, such as tungsten, lead, etc. A
spring washer 21 may be positioned at the top side 29a of the capsule 29,
between the capsule 29 and the shielding source holder 15. A circlip 22
may be positioned at the bottom side 29c of the capsule 29 to hold the
neutron source 11 in place. Top side 29a and bottom side 29c are labeled
relative to their positions in FIGS. 5A and 5B; however, the top and
bottom sides may be in various positions within a detector depending on
the direction of the detector. A press fit cover 23 may be placed within
the neutron source receiver 24 to cover the neutron source 11 and circlip
22.

[0035] Those of ordinary skill in the art will appreciate that shielding
source holder components may vary, depending on the size and shape of the
neutron source and detector. For example, shielding source holders made
according to the present disclosure may have various shapes and sizes
that position a shielding material between the neutron source and the
detector. Additionally, some embodiments of shielding source holders may
have additional components, less components, or different configurations
of the exemplary components described in FIGS. 5A and 5B, which may be
used to position the shielding source holder between the neutron source
and the detector.

[0036] The inventors of the present disclosure have found through testing
that shielding source holders according to embodiments of the present
disclosure produce results according to the theory presented above. In
particular, the inventors conducted experiments in which a detector
reading was produced for detector systems using various target materials,
gas-filled ion chambers, and shielding materials and control detector
systems using no target or no shielding material. The experiments show
that detector systems using shielding source holders according to the
present disclosure have low background (from gamma shielding) as well as
enhanced neutron signals. Neutron signal, as defined herein, is the
resulting signal determined by subtracting the amount of background from
the total signal reading. In an exemplary control test using a target
material made of polytetrafluoroethylene, a plastic having no hydrogen,
zero neutron signal was produced, thus showing neutron signals are
produced from hydrogen within target materials. Because the signal
produced from a detector system having no target also results in zero
neutron signal, target material having no hydrogen results in a neutron
signal equal to that of no target. A target made of material having no
hydrogen is referred to herein as a "blank target."

[0037] Referring now to FIG. 6, detector readings (produced in the form of
current) are shown for a moisture analyzer having a He-3-filled ion
chamber and a target made of polyethylene. Detector readings not related
to the target are considered background, while detector readings obtained
from the presence of the polyethylene target are considered as the total
signal. One reading was taken using a shielding source holder made of
tungsten; one reading was taken using a shielding source holder made of
lead; and another reading was taken using no shielding source holder. As
shown, shielding source holders made of lead, and especially tungsten,
suppress the background and at the same time increase the total signal.

[0038] The amount of background reduction and neutron signal enhancement
in embodiments according to the present disclosure was further analyzed
and compared with conventional detector systems. Data showing background
reduction is shown in Table 1 below and data showing neutron signal
enhancement is shown in FIG. 7 and Table 2 below.

[0039] In particular, as shown in Table 1, the amount of background from
gamma radiation is shown in a detector system having a He-3-filled ion
chamber and a detector system having a BF3-filled ion chamber,
wherein each detector system was tested with a tungsten shielding source
holder, a lead shielding source holder, and no shielding source holder.

[0040] As shown in Table 1, background from gamma radiation was reduced by
about 16% when using a shielding source holder made of tungsten in a
He-3-filled ion chamber and by about 47% when using a shielding source
holder made of tungsten in a BF3-filled ion chamber. Background from
gamma radiation was reduced by about 11% when using a shielding source
holder made of lead in a He-3-filled ion chamber and by about 39% when
using a shielding source holder made of lead in a BF3-filled ion
chamber.

[0041] Referring now to FIG. 7, neutron signal is enhanced by using
shielding source holders according to embodiments of the present
disclosure. In particular, detector systems having different gas-filled
ion chambers and different target materials each exhibited increased
neutron signals when using shielding source holders made of lead and
especially tungsten. The values of the neutron signals produced from each
detector system of FIG. 7 are shown in Table 2 below.

[0042] As shown in Table 2, the current readings (measured in pA) are
shown for detector systems having He-3- and BF3-filled ion chambers
and targets of different sizes and materials with and without shielding
source holders. Specifically, three sizes of polyethylene targets were
tested, medium, small, and extra small, and a water target was tested.
The larger polyethylene targets, which have more hydrogen, produced
larger neutron signals. Further, the neutron signals produced in detector
systems using lead shielding source holders each produced neutron signals
higher than in similar detector systems using no shielding source
holders. Likewise, the neutron signals produced in detector systems using
tungsten shielding source holders each produced neutron signals higher
than in similar detector systems using lead shielding source holders.
Thus, the inventors of the present disclosure have found that neutron
signal may be enhanced using shielding source holders made of lead and
especially tungsten.

[0043] The lead ratios and tungsten ratios show the amount of increase in
neutron flux when using a shielding source holder compared to detector
systems that do not use a shield. These exemplary results show an
increase in neutron flux in detector systems using shielding source
holders made of shielding material of the present disclosure.

[0044] The neutron signals for each case study shown above in Table 2 were
calculated by subtracting the signal detected using no target (or a blank
target) from the total signal detected using a target made of moderating
material. Table 3 shows exemplary calculations for the detector system
using a BF3-filled ion chamber and a medium-sized polyethylene
target.

[0045] As shown in Table 3, the neutron signal for a medium-sized
polyethylene target was calculated in detector system having no shield
and a tungsten shield. In particular, the neutron signals for each case
was calculated by subtracting the signal detected using no target (or a
blank target) from the total signal detected using a target made of
moderating material. The reading for the detector system having no
shielding source holder (1.004 pA) was lower than the reading for the
detector system having a shielding source holder made of tungsten (1.296
pA). Further, the readings show that the number of neutrons hitting the
detector is 1.29 times more with tungsten shielding than without. These
exemplary results show increased background readings in detector systems
having no shielding source holder and increased neutron signals in
detector systems having shielding source holders according to the present
disclosure.

[0046] Methods of measuring neutron signals using shielding source
holders, such as the ones described above, are also within the scope of
the present disclosure. In particular, improvements in producing neutron
signals while also decreasing gamma background, provided by shielding
source holders, may be measured using a three-phase experiment. In the
first phase, background is detected for a detector system with a
shielding source holder and without a shielding source holder. In
particular, background may be detected in a detector system having no
target, or alternatively, a blank target (i.e., a target made of material
containing no hydrogen), and with a shielding source holder surrounding a
portion of the neutron source. The shielding source holder may then be
removed and the detector system may be cleaned. Background may then be
detected in the cleaned detector system having no shielding source holder
surrounding the neutron source. It should be recognized that background
may be detected in a detector system with a shielding source holder
before or after background is detected in the detector system without a
shielding source holder.

[0047] In the second phase, a target material made of hydrogen-containing
material is placed within the detector system, and total signal is
measured for the detector system with and without the shielding source
holder. In particular, the total signal is measured for the detector
system with the shielding source holder used in phase one. The shielding
source holder may then be removed and the total signal is measured for
the detector system having no shielding source holder. It should be
recognized that total signal may be measured in the detector system with
a shielding source holder before or after total signal is measured in the
detector system without a shielding source holder.

[0048] In the third phase, neutron signal for the detector system with and
without a shielding source holder may be determined by subtracting the
background from the total signal, which were measured in phases one and
two, respectively. In particular, the neutron signal for the detector
system with a shielding source holder may be determined by subtracting
the background measured by the detector system with the shielding source
holder in phase one from the total signal measured by the detector system
with the shielding source holder in phase two. The neutron signal for the
detector system with no shielding source holder may be determined by
subtracting the background measured by the detector system with no
shielding source holder in phase one from the total signal measured by
the detector system with no shielding source holder in phase two.

[0049] A detector system used for the above described methods may include,
for example, an ion chamber detector, proportional counters, fission
chambers, or scintillator detectors. In particular, a detector system, or
analyzer, may include detector systems used to measure the hydrogen
content (e.g., moisture) in a sample (target). A shielding source holder
of the present disclosure made of shielding material, such as lead or
tungsten, may suppress unwanted background signal and at the same time
increase the neutron flux, thus increasing the useful signal.

[0050] Advantageously, increased neutron signals, and thus a higher
neutron flux, may allow for a reduced amount of time for detection and
moisture analysis. Inventors of the present disclosure have found that by
using shielding source holders made of tungsten, enhanced neutron signals
may be obtained while also decreasing the amount of background detected.
In particular, shielding source holders partially surround a neutron
source so as to shield gamma radiation released from the neutron source
from the detector.

[0051] While the present disclosure has been described with respect to a
limited number of embodiments, those skilled in the art, having benefit
of this disclosure, will appreciate that other embodiments may be devised
which do not depart from the scope of the disclosure as described herein.
Accordingly, the scope of the disclosure should be limited only by the
attached claims.